Mop assemblies of the type used for applying liquids (e.g., floor wax, polyurethane, or other floor finishing or floor sealing materials, disinfectants, etc.) to a surface such as the surface of a floor are known which include a mop head, a handle pivotally attached to the mop head by which the mop head can be manually moved along the surface; a valve assembly mounted on the handle adjacent the mop head connected by a hose to a supply of liquid supported above the mop head (e.g., in a back pack worn by the person using the mop), which valve is normally closed to stop the flow of liquid through the valve but can be manually opened to allow liquid from the container to flow through the valve and be deposited on the surface at a position close to the mop head from which the liquid can be spread over the surface by the mop head. Such mop assemblies are described in U.S. Pat. Nos. 4,119,386, 4,152,084, and 6,227,744, and in U.S. Patent Application Publication U.S. 2003/0197027 A1.
While such mop assemblies can be used effectively if they are thoroughly cleaned between each use, a significant problem can occur if certain liquids such as floor waxes or the like are allowed to remain in the valve assembly between uses. Such liquids can thicken and/or solidify when exposed to the atmosphere through the outlet opening of the valve, causing the valve to become sticky or even plugged because of the thickened or solidified material, and presenting a difficult clean up situation before the liquid delivery system on the mop will again operate properly.